In the fabrication of Nb3Sn superconducting wire, a barrier, usually tantalum or a tantalum alloy is employed to prevent tin contamination of the stabilizing copper on the exterior of the wire during heat treatment. The process is described in the article by David B. Smathers. While the porous metal sheath described in the present invention is similar to the barrier used in Nb3Sn conductor fabrication, application of the technology in this invention is entirely unique.